WO2021162017A1 - Solid-state imaging device - Google Patents

Abstract

A solid-state imaging device (200) is provided with: a photoelectric conversion unit (100) which comprises a plurality of pixel cells (10) arrayed in rows and columns, each of the plurality of pixel cells (10) generating charge by photoelectric conversion, and which holds a potential corresponding to the amount of the generated charge; an initialization unit (101) for initializing the potential of the photoelectric conversion unit (100); a comparison unit (102) which compares the potential of the photoelectric conversion unit (100) with a predetermined reference signal, and which, if the potential and the predetermined reference signal correspond to each other, causes the initialization unit (101) to perform initialization; and a counter unit (103) which counts the number of times of initialization performed by the initialization unit (101), and outputs a signal corresponding to the number of times as a first signal indicating the intensity of incident light.

Description

Solid-state image sensor

This disclosure relates to a solid-state image sensor.

Patent Document 1 discloses a pulse modulation method as a method for detecting the light intensity of a CMOS type image sensor. As a pulse modulation method, a pulse width modulation (PWM) method and the like have been introduced. The PWM method is a method in which the intensity of incident light is reflected in the pulse width.

Japanese Unexamined Patent Publication No. 2005-252743

However, higher speed and higher accuracy are desired compared to the conventional solid-state image sensor.

The present disclosure provides a solid-state image sensor capable of increasing speed and accuracy.

The solid-state imaging device according to one aspect of the present disclosure includes a plurality of pixel cells arranged in a matrix, and each of the plurality of pixel cells generates an electric charge by photoelectric conversion, and corresponds to the amount of the generated electric charge. The photoelectric conversion unit that holds the potential, the initialization unit that initializes the potential of the photoelectric conversion unit, the potential of the photoelectric conversion unit is compared with a predetermined reference signal, and when they match, the initialization unit is initialized. It includes a comparison unit for executing the conversion, and a counter unit for counting the number of initializations executed by the initialization unit and outputting a signal corresponding to the number of times as a first signal indicating the intensity of incident light.

According to the solid-state image sensor according to the present disclosure, high speed and high accuracy can be achieved.

FIG. 1A is a diagram showing a schematic configuration of a solid-state image sensor according to an embodiment. FIG. 1B is an operation explanatory view of the solid-state image sensor of FIG. 1A. FIG. 2A is a diagram showing a configuration example of the solid-state image sensor according to the first embodiment. FIG. 2B is a diagram showing another configuration example of the pixel cell in FIG. 2A. FIG. 2C is a circuit diagram showing an example of an SF circuit in FIG. 2B. FIG. 3 is a time chart showing an operation example of the solid-state image sensor according to the first embodiment. FIG. 4 is a diagram showing a configuration example of the solid-state image sensor according to the second embodiment. FIG. 5 is a time chart showing an operation example of the solid-state image sensor according to the second embodiment. FIG. 6A is a diagram showing a configuration example of the solid-state image sensor according to the third embodiment. FIG. 6B is a diagram showing another configuration example of the solid-state image sensor according to the third embodiment. FIG. 7 is a time chart showing an operation example of the solid-state image sensor according to the third embodiment. FIG. 8 is a diagram showing a configuration example of the solid-state image sensor according to the fourth embodiment. FIG. 9 is a diagram showing a configuration example of the solid-state image sensor according to the fifth embodiment. FIG. 10 is a time chart showing an operation example of the solid-state image sensor according to the fifth embodiment. FIG. 11A is a diagram showing a configuration example of the solid-state image sensor according to the sixth embodiment. FIG. 11B is a diagram showing a voltage waveform generated by the taper voltage generation unit of FIG. 11A. FIG. 12 is a diagram showing a configuration example of the solid-state image sensor according to the seventh embodiment.

First, an outline of the solid-state image sensor according to one aspect of the present disclosure will be described.

The solid-state imaging device according to one aspect of the present disclosure includes a plurality of pixel cells arranged in a matrix, and each of the plurality of pixel cells generates an electric charge by photoelectric conversion, and corresponds to the amount of the generated electric charge. The photoelectric conversion unit that holds the potential, the initialization unit that initializes the potential of the photoelectric conversion unit, the potential of the photoelectric conversion unit is compared with a predetermined reference signal, and when they match, the initialization unit is initialized. It includes a comparison unit for executing the conversion, and a counter unit for counting the number of initializations executed by the initialization unit and outputting a signal corresponding to the number of times as a first signal indicating the intensity of incident light.

According to this, the first signal can be generated as a digital signal, and speeding up is easy. Further, even when the incident light is so strong that the amount of charge generated by the photoelectric conversion greatly exceeds the saturated charge amount of the photoelectric conversion unit 100, the image is taken with initialization, so that the image can be accurately captured even in a very bright scene. Can be done.

For example, the solid-state image sensor further comprises an AD conversion unit that AD-converts the potential of the photoelectric conversion unit after the last initialization and outputs the AD-converted data as a second signal indicating the intensity of the incident light. You may prepare.

According to this, the electric charge remaining in the photoelectric conversion unit without being initialized after the last initialization is AD-converted and output as a second signal. Since the second signal corresponds to the amount of electric charge less than one count of the first signal, the intensity of the incident light can be obtained with higher accuracy.

For example, the AD conversion unit may be provided for each pixel cell.

According to this, a global shutter can be easily realized.

For example, the AD conversion unit may be provided for each of a predetermined number of pixel cells.

According to this, if a predetermined number of pixel cells are pixel cells for each column, a rolling shutter can be easily realized.

For example, the solid-state image sensor may further include a signal processing unit that generates a third signal indicating the intensity of incident light by synthesizing the first signal and the second signal.

According to this, both high speed and high accuracy can be achieved at the same time. Regarding speeding up, the frame rate can be easily increased by reducing the number of bits in the counter unit to limit the maximum count value, that is, by limiting the number of countable initializations within one frame period. Even if the number of bits of the counter unit is limited in this way, the accuracy is improved by the second signal, so that both high speed and high accuracy can be easily realized.

For example, each of the plurality of pixel cells may further include a feedback circuit that feeds back the potential of the photoelectric conversion unit to the photoelectric conversion unit via the initialization unit at the time of initialization by the initialization unit. good.

According to this, by initializing the potential of the photoelectric conversion unit by feedback, kTC noise at the time of initialization can be reduced. As a result, good imaging with less noise is possible even in a dark scene.

For example, the feedback circuit may include an amplification unit that outputs the difference between the voltage of the photoelectric conversion unit and a predetermined voltage to the initialization unit as an initial voltage.

According to this, a feedback path can be configured via the amplification unit.

For example, the initialization unit includes a transistor, one of the source and drain of the transistor is connected to the photoelectric conversion unit, the other of the source and drain of the transistor is input with an initial voltage, and the gate of the transistor is input. Is connected to an output line showing the comparison result of the comparison unit, and the amplification unit may include an amplifier that outputs the difference between the voltage of the photoelectric conversion unit and the predetermined voltage as the initial voltage to the drain of the transistor. ..

According to this, since the initialization unit is composed of transistors, the initialization operation can be easily controlled to an appropriate speed. Also, the feedback loop can be configured with a simple circuit.

For example, the initialization unit includes a transistor, one of the source and drain of the transistor is connected to the photoelectric conversion unit, the other of the source and drain of the transistor is input with an initial voltage, and the gate of the transistor is input. May be connected to an output line indicating the comparison result of the comparison unit.

According to this, since the initialization unit is composed of transistors, the initialization operation can be easily controlled to an appropriate speed.

For example, in each of the plurality of pixel cells, when the output line indicating the comparison result of the comparison unit is inverted, the initialization unit is made to perform initialization, and the potential of the photoelectric conversion unit is set to the above. An initialization control unit that feeds back to the photoelectric conversion unit via the initialization unit may be provided.

According to this, it is possible to easily control at the same time without causing a timing difference between the control of the initialization unit and the control of the feedback.

For example, each of the plurality of pixel cells further includes an overflow drain unit for discharging charges and a transfer transistor for transferring a charge exceeding a predetermined amount of the photoelectric conversion unit to the overflow drain unit. The potential of may be input to the comparison unit as the potential of the photoelectric conversion unit.

According to this, the number of elements connected to the photoelectric conversion unit can be reduced, the amount of voltage per generated charge can be improved, and for example, the influence of noise in the AD conversion unit can be relatively suppressed. Can be done.

For example, the solid-state image sensor further generates a taper voltage whose voltage changes with the passage of time when a signal indicating that the potential of the photoelectric conversion unit and a predetermined reference signal match is input from the comparison unit. However, it may be provided with a taper voltage generation unit that supplies the gate of the transition.

According to this, kTC noise in the initialization operation can be suppressed. As a result, good imaging with less noise is possible even in a dark scene.

For example, the solid-state image sensor includes a first semiconductor substrate having the photoelectric conversion unit and a second semiconductor substrate having the counter unit, and the first semiconductor substrate and the second semiconductor substrate may be laminated.

According to this, the solid-state image sensor 200 can be miniaturized due to the laminated structure.

For example, the solid-state image sensor includes a first semiconductor substrate having the photoelectric conversion unit and a second semiconductor substrate having the AD conversion unit, and the first semiconductor substrate and the second semiconductor substrate may be laminated. ..

According to this, the solid-state image sensor 200 can be miniaturized due to the laminated structure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. It should be noted that all of the embodiments described below show a specific example of the present disclosure. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, drive timings, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept of the present disclosure will be described as arbitrary components. Moreover, each figure is not necessarily exactly illustrated. In each figure, duplicate description will be omitted or simplified for substantially the same configuration.

Next, a schematic configuration of the solid-state image sensor according to one aspect of the present disclosure will be described.

FIG. 1A is a diagram showing a schematic configuration of a solid-state image sensor 200 according to an embodiment. Further, FIG. 1B is an operation explanatory view of the solid-state image sensor 200 of FIG. 1A.

As shown in FIG. 1A, the solid-state image sensor 200 includes a plurality of pixel cells 10 arranged in a matrix. Each of the plurality of pixel cells 10 has a photoelectric conversion unit 100, an initialization unit 101 that initializes the photoelectric conversion unit 100, and a counter unit 103.

The photoelectric conversion unit 100 generates an electric charge by the photoelectric conversion and holds a potential corresponding to the amount of the generated electric charge. As shown in FIG. 1B, for example, the potential of the photoelectric conversion unit 100 decreases with the passage of time from the initial voltage because an electric charge is generated according to the amount of incident light.

The initialization unit 101 initializes to the initial voltage when the voltage of the photoelectric conversion unit 100 drops to the reference voltage. For example, the initialization unit 101 is turned on at the timing of the arrow line in FIG. 1B when the potential of the photoelectric conversion unit 100 drops to the reference voltage, and the photoelectric conversion unit 100 is initialized. The initial voltage may be, for example, the power supply voltage Vdd or a predetermined voltage value. Since the initialization to the initial voltage, the initialization unit 101 is turned off and the initialization is canceled.

The counter unit 103 counts the number of times the initialization unit 101 initializes the photoelectric conversion unit 100, and outputs a signal corresponding to the number of times as a first signal indicating the intensity of the incident light. In the example of FIG. 1B, the counter unit 103 starts the counting operation from the initial value 0 and counts up to 3. The digital signal OUT1 is an example of the first signal, and in FIG. 1B, it is a digital value showing the value of 3.

In this way, the solid-state image sensor 200 generates a digital signal OUT1 for each pixel cell. As a result, high-speed imaging becomes possible, and even in a state where the photoelectric conversion unit 100 is irradiated with light that is so strong that the photoelectric conversion unit 100 cannot perform photoelectric conversion (that is, the amount of charge due to photoelectric conversion exceeds the saturated charge amount). Since the photoelectric conversion unit 100 generates a digital signal while being initialized, it is possible to take an image even in a bright scene that exceeds the conversion capacity of the photoelectric conversion unit 100.

(Embodiment 1)
In the first embodiment, a more specific configuration example of the solid-state image sensor 200 will be described. FIG. 2A is a diagram showing a configuration example of the solid-state image sensor 200 according to the second embodiment. FIG. 3 is a time chart showing an operation example of the solid-state image sensor 200 shown in FIG. 2A.

As shown in FIGS. 2A and 3, in the solid-state image sensor 200 according to the present embodiment, the pixel cell 10 further has a comparison unit 102 with respect to the solid-state image sensor 200 shown in FIG. 1A. The solid-state image sensor 200 is different in that it further includes a reset voltage generation unit 20 connected to the pixel cell 10, a REF voltage generation unit 30, and a count control signal generation unit 40. In addition, REF means a reference signal for comparison. Hereinafter, the differences will be mainly described while avoiding duplication of explanation.

The comparison unit 102 compares the potential of the photoelectric conversion unit 100 with the predetermined reference signal REF, and causes the initialization unit 101 to execute initialization when they match. Specifically, the comparison unit 102 compares the high-low relationship between the voltage of the output signal PD of the photoelectric conversion unit 100 and the voltage of the reference signal REF output by the REF voltage generation unit 30, and determines the voltage of the output signal PD. If the value is higher, the low level is output, and if it is not higher, the high level is output as the reset signal RST.

The reset voltage generation unit 20 generates an output signal VINI. The output signal VINI may be, for example, the power supply voltage VDD or another voltage value. The output signal VINI is supplied to the photoelectric conversion unit 100 as an initial voltage or a reset voltage via the initialization unit 101.

The REF voltage generation unit 30 generates a reference signal REF. The reference signal REF may be, for example, a voltage value of the photoelectric conversion unit 100 when the electric charge held in the photoelectric conversion unit 100 is saturated, or a voltage value between the voltage value and the power supply voltage VDD. You may.

The count control signal generation unit 40 generates a count initialization signal INIT and a count stop signal STOP in order to control the counter unit 103. The count initialization signal INIT is a control signal for initializing the count value of the counter unit 103 to 0. The count stop signal STOP is a signal that controls whether to operate or stop the counting operation of the counter unit 103.

The time chart of FIG. 3 shows the imaging operation for two frames. The first frame corresponds to a relatively strong incident light, and the second frame corresponds to a relatively weak incident light.

As shown in FIG. 3, when the reset signal RST is at a high level, the initialization unit 101 initializes the output signal PD of the photoelectric conversion unit 100 to the output signal VINI output by the reset voltage generation unit 20.

When the count stop signal STOP output by the count control signal generation unit 40 is low level, the counter unit 103 counts the number of times the reset signal RST transitions from low level to high level, and counts the count result OUT. When the count stop signal STOP is at a high level, the signal is stopped in the counted state, and when the count initialization signal INIT is at a high level, the count value is initialized to 0.

Further, by setting the reference signal REF to a power supply voltage VDD higher than the output signal VINI, the reset signal RST becomes a high level, the photoelectric conversion unit 100 is initialized, and the count initialization signal INIT and the count stop signal STOP are set to high. By setting the level, the count signal OUT1 is initialized to 0.

Further, by setting the count initialization signal INIT and the count stop signal STOP to a low level and setting the reference signal REF to a voltage lower than the output signal VINI, the reset signal RST becomes a low level and the initialization is stopped. The voltage of the output signal PD drops from the output signal VINI at a speed corresponding to the amount of light irradiation, and when the voltage of the output signal PD reaches the voltage REF, the reset signal RST transitions to a high level and the count signal. When OUT becomes 1, the photoelectric conversion unit 100 is initialized, the voltage of the output signal PD becomes the output signal VINI, and the reset signal RST becomes the low level.

Further, the voltage of the output signal PD decreases from the output signal VINI at a speed corresponding to the amount of light irradiation, and when the voltage VERF is reached, the reset signal RST transitions to a high level and the count signal OUT becomes 2. At the same time, the photoelectric conversion unit 100 is initialized, and the voltage of the output signal PD becomes the output signal VINI.

Further, when the count stop signal STOP becomes high level, the count signal keeps the count value at that time, and is digital according to the amount of light emitted to the photoelectric conversion unit 100 for each pixel cell. Generate signal OUT1.

As described above, the solid-state image sensor 200 according to the present embodiment described with reference to FIGS. 2A and 3 resets when a certain amount of electric charge is accumulated, and outputs the number of resets as a digital value. The solid-state image sensor 200 can perform high-speed imaging by generating a digital signal for each pixel cell. Further, even in a state where the photoelectric conversion unit 100 is irradiated with light that is so strong that it cannot be photoelectrically converted, the photoelectric conversion unit 100 generates a digital signal while being initialized, so that the conversion capability of the photoelectric conversion unit 100 can be improved. Imaging is possible even in brighter scenes.

Further, since the photoelectric conversion unit 100 can take an image with initialization even if the light receiving area is reduced, the solid-state image sensor 200 can be miniaturized and the cost can be reduced.

If the number of bits of the counter unit 103 is M bits, the number of initializations can be ^{counted up to (2 M} -1) times. M may be determined according to, for example, the difference between VINI and REF.

Note that the pixel cell 10 may include an SF (source follower) circuit 108 as shown in FIG. 2B. FIG. 2C shows a configuration example of the SF circuit 108. As shown in FIG. 2C, the SF circuit 108 includes an amplification transistor 108a and a current source 108b. The amplification transistor 108a converts the potential generated by the electric charge of the photoelectric conversion unit 100 into a voltage and outputs it to the comparison unit 102. The current source 108b is a load that supplies a load current to the amplification transistor 108a, and can be composed of, for example, a resistance element, a diode, a drundista, or the like. By configuring as shown in FIG. 2B, it is possible to suppress the electric charge of the photoelectric conversion unit 100 from being destroyed and stabilize the operation.

(Embodiment 2)
In the second embodiment, a solid-state image sensor capable of higher accuracy than the first embodiment by the configuration including the AD conversion unit 50 will be described.

FIG. 4 is a diagram showing a configuration example of the solid-state image sensor 200 according to the second embodiment. FIG. 5 is a time chart diagram showing an operation example of the solid-state image sensor 200 shown in FIG.

From FIGS. 4 and 5, the solid-state image sensor 200 according to the present embodiment has an AD conversion unit 50 connected to the pixel cell 10 and a digital signal processing unit 60 with respect to the solid-state image sensor 200 shown in FIG. 2A. The difference is that it has. Hereinafter, the differences will be mainly described while avoiding duplication of explanation.

The AD conversion unit 50 AD-converts the potential of the photoelectric conversion unit 100 after it is finally initialized in the frame, and outputs the AD-converted data as a second signal indicating the intensity of the incident light. Specifically, the AD conversion unit 50 outputs a digital signal OUT2 corresponding to the voltage of the output signal PD after the counter unit 103 has stopped counting. The AD conversion unit 50 may be, for example, a single slope type AD converter. Further, the AD conversion unit 50 may be another method such as a sequential comparison method.

The digital signal processing unit 60 generates a digital signal OUT3 which is a third signal indicating the intensity of the incident light by synthesizing the count signal OUT1 which is the first signal and the digital signal OUT2 which is the second signal. For example, the digital signal processing unit 60 combines the count signal OUT1 and the digital signal OUT2 to generate a new digital signal OUT3. In the example of FIG. 5, the count signal OUT1 is 5 and the digital signal OUT2 is 6. It is assumed that the AD conversion unit 50 has 4 bits and a resolution of 16. The counter unit 103 is assumed to be a resolution ^{2 12} 12 bits. In this case, the digital signal OUT3 becomes the resolution ^{2 16} 16-bit. The digital signal OUT3 is (16 × count signal OUT1 + digital signal OUT2) = (16 × 5 + 6) = 96.

Assuming that the number of bits of the counter unit 103 is M and the number of bits of the AD conversion unit 50 is L, the number of bits of the digital signal OUT3 is M + L bits.

Note that the digital signal processing unit 60 may simply concatenate the M-bit data of the count signal OUT1 and the L-bit data of the digital signal OUT2 as MSB-side data and LSB-side data.

Further, the digital signal processing unit 60 calculates the M bit data of the count signal OUT1 and the L bit data of the digital signal OUT2 as MSB side data and LSB side data, and a digital signal having a smaller number of bits than (M + L). It may be combined with the data of OUT3.

On the contrary, the digital signal processing unit 60 calculates the M bit data of the count signal OUT1 and the L bit data of the digital signal OUT2 as MSB side data and LSB side data, and digitally has a larger number of bits than (M + L). It may be combined with the data of the signal OUT3.

As described above, the solid-state image sensor according to the present embodiment described with reference to FIGS. 4 and 5 performs AD conversion of the residual and digitally outputs the residual together with the number of resets. As a result, it is possible to output a higher-definition digital signal according to the amount of light irradiation, and it is possible to perform good imaging that reproduces brightness and hue closer to the outside world.

The AD conversion unit 50 may be provided for each pixel cell 10. In this way, the global shutter can be easily realized.

Further, the AD conversion unit 50 may be provided for every predetermined number of pixel cells 10. The predetermined number of pixel cells 10 may be every pixel cell 10 belonging to the same column. If a predetermined number of pixel cells are pixel cells for each column, a so-called rolling shutter can be easily realized.

Note that, in FIG. 5, the digital signal processing unit 60 may perform CDS (correlation double sampling) in the AD conversion of the residuals. Further, the digital signal processing unit 60 may perform CDS using the AD conversion unit 50 in each section from the initialization of the output signal PD other than the residual to the next initialization. Further, it may be determined in advance or dynamically selectively whether or not to perform CDS in each section. For example, CDS may be performed on the output signal PD up to the first initialization, or CDS may be performed only when the illuminance is low.

(Embodiment 3)
In the third embodiment, a configuration including a feedback circuit for feeding back the potential of the photoelectric conversion unit 100 to the photoelectric conversion unit 100 via the initialization unit 101 at the time of initialization by the initialization unit 101 will be described. The feedback of the initial voltage can cancel the kTC noise at the time of initialization.

FIG. 6A is a diagram showing a configuration example of the solid-state image sensor 200 according to the embodiment. FIG. 7 is a time chart showing an operation example of the solid-state image sensor 200 shown in FIG. 6A.

From FIGS. 6A and 7, in the solid-state image sensor 200 according to the present embodiment, the pixel cell 10 is inverted with the inversion amplification unit 104 instead of the comparison unit 102 with respect to the solid-state image sensor 200 shown in FIG. 2A. The difference is that it has an amplification unit 105 and a feedback circuit including an inverting amplification unit 105 into which the output signal VINI of the reset voltage generation unit 20 is input.

The inverting amplification unit 104 is an operational amplifier, and like the comparison unit 102, compares the voltage of the output signal PD of the photoelectric conversion unit 100 with the voltage of the reference signal REF output by the REF voltage generation unit 30. When the voltage of the output signal PD is higher, the low level is output, and when the voltage is lower, the high level is output as the reset signal RST.

Further, the inverting amplification unit 105 is an operational amplifier, and constitutes a feedback circuit that feeds back the potential of the photoelectric conversion unit 100 to the photoelectric conversion unit 100 via the initialization unit 101 at the time of initialization by the initialization unit 101. Specifically, the inverting amplification unit 105 amplifies and outputs the difference between the voltage of the output signal PD and the output signal VINI of the signal output by the reset voltage generation unit 20.

As described above, the solid-state image sensor according to the present embodiment described with reference to FIGS. 6A and 7 performs feedback reset. By generating a digital signal for each pixel cell by these configurations and drives, high-speed imaging becomes possible, and further, a state in which the photoelectric conversion unit 100 is irradiated with light that is so strong that photoelectric conversion is impossible. However, since the photoelectric conversion unit 100 generates a digital signal while being initialized, it is possible to take an image even in a bright scene that exceeds the conversion capacity of the photoelectric conversion unit 100. Further, by adding the inverting amplification unit 105 and feeding back the amplified signal for initialization, noise at the time of initialization can be reduced. As shown in FIG. 7, each of the output signal PDs immediately after initialization can be aligned to a level with less variation due to noise. As a result, good imaging with less noise is possible even in a dark scene.

As shown in FIG. 6B, the pixel cell 10 of FIG. 6A may be configured to include a transfer transistor 109, an overflow drain portion 110, and an overflow drain control transistor 111.

The transfer transistor 109 is a transfer transistor that transfers an electric charge exceeding a predetermined amount of the photoelectric conversion unit 100 to the overflow drain unit 110. The gate of the transfer transistor 109 is set with a voltage Vov that allows charges exceeding a predetermined amount to pass through.

The overflow / drain unit 110 is a charge discharge port that is set to the voltage Vd when the overflow / drain control transistor 111 is in the ON state. The voltage Vd may be, for example, the power supply voltage Vdd or another voltage value.

According to FIG. 6B, by turning off the overflow drain control transistor 111 during the photoelectric conversion period, the voltage of the overflow drain unit 110 changes in response to the electric charge overflowing from the photoelectric conversion unit 100. When the potential of the overflow / drain unit 110 drops to the voltage of the reference signal REF, the inverting amplification unit 104 and the initialization unit 101 reset the photoelectric conversion unit 100. As a result, the number of elements connected to the photoelectric conversion unit 100 can be reduced, the amount of voltage per generated charge can be improved, and for example, the influence of noise in the AD conversion unit 50 can be relatively suppressed. ..

(Embodiment 4)
In the fourth embodiment, a configuration example in which the second embodiment and the third embodiment are combined will be described.

FIG. 8 is a diagram showing a configuration example of the solid-state image sensor 200 according to the fourth embodiment. The solid-state image sensor 200 of FIG. 8 includes the pixel cell 10 of FIG. 6A of the third embodiment instead of the pixel cell 10 of FIG. 4 of the second embodiment.

The solid-state imaging device 200 shown in FIG. 8 includes an AD conversion unit 50 connected to the pixel cell 10 and a digital signal processing unit 60, and the AD conversion unit 50 outputs after the counter unit 103 stops counting. The digital signal OUT2 corresponding to the voltage of the signal PD is output, and the digital signal processing unit 60 combines the count signal OUT and the digital signal OUT2 to generate a new digital signal OUT3.

Further, in the solid-state image sensor 200 shown in FIG. 8, in addition to the feedback reset, the residual is AD-converted and digitally output together with the number of resets, whereby higher definition is obtained according to the amount of light irradiation. Digital signals can be output, and imaging that reproduces brightness and hue closer to the outside world becomes possible.

(Embodiment 5)
In the fifth embodiment, when the output line indicating the comparison result of the comparison unit is inverted, the initialization unit 101 is made to execute the initialization, and the potential of the photoelectric conversion unit 100 is photoelectrically converted via the initialization unit 101. An example of the configuration for feeding back to the unit 100 will be described.

FIG. 9 is a diagram showing a configuration example of the solid-state image sensor 200 according to the fifth embodiment. FIG. 10 is a time chart showing an operation example of the solid-state image sensor 200 shown in FIG.

From FIGS. 9 and 10, the solid-state image sensor 200 according to the present embodiment has the solid-state image sensor 200 shown in FIG. 1A, and the pixel cell 10 further includes an amplification unit 106 and an initialization control unit 107. The solid-state image sensor 200 further includes a reset voltage generation unit 20, a REF voltage generation unit 30, a count control signal generation unit 40, an AD conversion unit 50, and a digital signal connected to the pixel cell 10. It includes a processing unit 60 and an initialization control unit 107.

Further, the amplification unit 106 amplifies and outputs the difference between the voltage of the output signal PD of the photoelectric conversion unit 100 and the voltage of the reference signal REF2 output by the REF voltage generation unit 30.

Further, when the initialization selection signal SEL output from the initialization control unit 107 is at a low level, the initialization control unit 107 sets the output signal CNT of the amplification unit 106 to the input signal SET to the initialization unit 101. When the initialization signal CTL output from the initialization control unit 107 is connected to the reset signal RST to the initialization unit 101 and the initialization selection signal SEL is at a high level, the output signal is output. The CNT is connected to the reset signal RST, and the initialization voltage signal INI2 output from the initialization control unit 107 is connected to the input signal SET.

Further, when the reset signal RST is at a high level, the initialization unit 101 initializes the voltage of the output signal PD by connecting the output signal PD of the photoelectric conversion unit 100 to the input signal SET, and the reset signal RST is at a low level. In the case of, the output signal PD is put into a floating state by separating the input signal SET and the output signal PD.

Further, the counter unit 103 counts the number of times the reset signal RST transitions from the low level to the high level when the count stop signal STOP output by the count control signal generation unit 40 is low level, and counts the count result. It is output to OUT, and when the count stop signal STOP is high level, it stops in the counted state, and when the count initialization signal INI becomes high level, the count value is initialized to 0.

Further, by setting the reference signal REF2 as the output signal VINI, the initialization selection signal SEL as the low level, and the initialization signal CTL as the high level, the photoelectric conversion unit 100 is initialized to the output signal VINI and the count is initialized. By setting the signal INT and the count stop signal STOP to a high level, the count signal OUT is initialized to 0.

Further, by setting the count initialization signal INI and the count stop signal STOP to a low level, setting the reference signal REF to a voltage VERF lower than the output signal VINI, and setting the initialization selection signal SEL to a high level, the amplification unit 106 The feedback path between the input and output of is cut off, the amplification unit 106 acts as a comparison unit substantially, the output signal CNT becomes low level, initialization is stopped, and the voltage of the output signal PD is irradiated with light. When the output signal VINI drops at a speed corresponding to the amount and the voltage of the output signal PD reaches the voltage VERF, the reset signal RST transitions to a high level, the count signal OUT becomes 1, and the photoelectric signal becomes 1. The conversion unit 100 is initialized, the voltage of the output signal PD becomes the output signal VINI2 of the count initialization signal INI2, and the reset signal RST becomes a low level.

Further, the voltage of the output signal PD decreases from the output signal VINI at a speed corresponding to the amount of light irradiation, and when the voltage VERF is reached, the output signal CNT transitions to a high level, the count signal OUT becomes 2, and the count signal OUT becomes 2. The photoelectric conversion unit 100 is initialized, and the voltage of the output signal PD becomes the output signal VINI2.

Further, the count stop signal STOP becomes high level, and the count signal keeps the count value at that time according to the amount of light emitted to the photoelectric conversion unit 100 for each pixel cell. Generates a digital signal.

As described above, the solid-state image sensor according to the present embodiment described with reference to FIGS. 9 and 10 shares the comparison unit and the inverting amplification unit, and by these configurations and drives, a digital signal is generated for each pixel cell. As a result, high-speed imaging becomes possible, and even in a state where the photoelectric conversion unit 100 is irradiated with light that is too strong to be photoelectrically converted, the photoelectric conversion unit 100 generates a digital signal while being initialized. Therefore, it is possible to take an image even in a bright scene that exceeds the conversion capacity of the photoelectric conversion unit 100. In addition, by setting and driving only the initial initialization by feeding back the amplified signal to initialize it, it is possible to perform good imaging with less noise only in dark scenes where low noise is required, and the components. By reducing the noise consumption and reducing the pixel size, spatially higher definition imaging becomes possible.

(Embodiment 6)
In the sixth embodiment, a configuration example in which a tapered gate signal is supplied to the gate of the transistor constituting the initialization unit 101 will be described.

FIG. 11A is a diagram showing a configuration example of the solid-state image sensor according to the sixth embodiment. Further, FIG. 11B is a diagram showing a voltage waveform generated by the taper voltage generation unit 70 of FIG. 11A.

FIG. 11A is different from FIG. 8 in that the taper voltage generation unit 70 is added. The differences will be mainly described below.

The taper voltage generation unit 70 outputs a tapered voltage whose voltage changes with the passage of time when a signal indicating that the potential of the photoelectric conversion unit 100 and a predetermined reference signal match is input from the inverting amplification unit 104. It is generated and supplied to the transition gate of the initialization unit 101.

As a result, the solid-state image sensor 200 according to the sixth embodiment is switched by using a signal whose voltage changes at a constant rate with the passage of time by limiting the band at the time of initialization of the photoelectric conversion unit 100. By the taper reset that controls ON / OFF, the effect of reducing the amount of noise superimposed on the output signal PD of the photoelectric conversion unit 100 is increased, and even in a dark scene, good imaging with less noise becomes possible.

(Embodiment 7)
In the seventh embodiment, an example in which the solid-state image sensor 200 is composed of two semiconductor substrates on which the solid-state image pickup device 200 is laminated will be described.

FIG. 12 is a diagram showing a configuration example of the solid-state image sensor 200 according to the embodiment. In the solid-state image sensor 200 shown in the figure, the first semiconductor substrate 201 having the photoelectric conversion unit 100 and the second semiconductor substrate 202 having the counter unit 103 are laminated with each other. It is electrically connected.

From FIG. 12, the photoelectric conversion unit 100 and the counter unit 103 are provided on different semiconductor substrates. As the photoelectric conversion unit 100 and the counter unit 103, any of the solid-state image pickup devices 200 described in FIGS. 1A to 11B can be used.

As a result, by stacking and arranging the photoelectric conversion unit 100 and the counter unit 103, the area of the cell per pixel can be reduced, and more spatially high-definition imaging becomes possible.

The second semiconductor substrate 202 may include an AD conversion unit 50.

The ranging imaging device according to the present disclosure can be used for, for example, a camera and a ranging sensor.

10 Pixel cell 20 Reset voltage generation unit 30 REF voltage generation unit 40 Count control signal generation unit 50 AD conversion unit 60 Digital signal processing unit 70 Tapered voltage generation unit 100 Photoelectric conversion unit 101 Initialization unit 102 Comparison unit 103 Counter unit 104 Inverted amplification Unit 105 Inversion amplification unit 106 Amplification unit 107 Initialization control unit 108 SF circuit 108a Amplification transistor 108b Current source 109 Transfer transistor 110 Overflow drain unit 111 Overflow drain control transistor 200 Solid-state imaging device 201 First semiconductor substrate 202 Second semiconductor substrate

Claims (14)

It has multiple pixel cells arranged in a matrix.
Each of the plurality of pixel cells
A photoelectric conversion unit that generates electric charges by photoelectric conversion and holds an electric potential according to the amount of generated charges.
An initialization unit that initializes the potential of the photoelectric conversion unit,
A comparison unit that compares the potential of the photoelectric conversion unit with a predetermined reference signal and causes the initialization unit to perform initialization when they match.
A solid-state image sensor including a counter unit that counts the number of initializations executed by the initialization unit and outputs a signal corresponding to the number of times as a first signal indicating the intensity of incident light. The first aspect of the present invention includes an AD conversion unit that AD-converts the potential of the photoelectric conversion unit after the last initialization and outputs the AD-converted data as a second signal indicating the intensity of the incident light. Solid-state image sensor. The solid-state image sensor according to claim 2, wherein the AD conversion unit is provided for each pixel cell. The solid-state image sensor according to claim 2, wherein the AD conversion unit is provided for each of a predetermined number of pixel cells. The solid-state imaging according to any one of claims 2 to 4, further comprising a signal processing unit that generates a third signal indicating the intensity of incident light by synthesizing the first signal and the second signal. Device. Each of the plurality of pixel cells further
The solid-state imaging according to any one of claims 1 to 5, further comprising a feedback circuit that feeds back the potential of the photoelectric conversion unit to the photoelectric conversion unit via the initialization unit at the time of initialization by the initialization unit. Device. The solid-state image sensor according to claim 6, wherein the feedback circuit includes an amplification unit that outputs a difference between the voltage of the photoelectric conversion unit and a predetermined voltage to the initialization unit as an initial voltage. The initialization unit includes a transistor and includes a transistor.
One of the source and drain of the transistor is connected to the photoelectric conversion unit, and the transistor is connected to the photoelectric conversion unit.
An initial voltage is input to the other of the source and drain of the transistor.
The gate of the transistor is connected to an output line showing the comparison result of the comparison unit, and is connected to the output line.
The solid-state image sensor according to claim 7, wherein the amplification unit includes an amplifier that outputs a difference between the voltage of the photoelectric conversion unit and a predetermined voltage as the initial voltage to the drain of the transistor. The initialization unit includes a transistor and includes a transistor.
One of the source and drain of the transistor is connected to the photoelectric conversion unit, and the transistor is connected to the photoelectric conversion unit.
An initial voltage is input to the other of the source and drain of the transistor.
The solid-state image sensor according to any one of claims 1 to 6, wherein the gate of the transistor is connected to an output line showing a comparison result of the comparison unit. Each of the plurality of pixel cells further
When the output line indicating the comparison result of the comparison unit is inverted, the initialization unit is made to execute initialization, and the potential of the photoelectric conversion unit is fed back to the photoelectric conversion unit via the initialization unit. The solid-state imaging device according to any one of claims 1 to 5, further comprising an initialization control unit. Each of the plurality of pixel cells further
Overflow drain for charge discharge and
A transfer transistor that transfers a charge exceeding a predetermined amount of the photoelectric conversion unit to the overflow drain unit is provided.
The solid-state image sensor according to any one of claims 1 to 10, wherein the potential of the overflow drain unit is input to the comparison unit as the potential of the photoelectric conversion unit. Further, when a signal indicating that the potential of the photoelectric conversion unit and a predetermined reference signal match is input from the comparison unit, a taper voltage whose voltage changes with the passage of time is generated at the gate of the transistor. The solid-state imaging device according to claim 8 or 9, further comprising a taper voltage generator for supplying. The first semiconductor substrate having the photoelectric conversion unit and
A second semiconductor substrate having the counter unit is provided.
The solid-state image sensor according to any one of claims 1 to 12, wherein the first semiconductor substrate and the second semiconductor substrate are laminated. The first semiconductor substrate having the photoelectric conversion unit and
A second semiconductor substrate having the AD conversion unit is provided.
The solid-state image sensor according to any one of claims 2 to 4, wherein the first semiconductor substrate and the second semiconductor substrate are laminated.

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